Various types of sequential punching apparatus are known, in which metallic strip, ribbon, tape or the like is guided, in cadence with operation of the punching apparatus, along a predetermined path. Upon each reciprocating punching movement of the punch itself, the metal ribbon is advanced by one step. The punches themselves are located above the metal ribbon, movable towards and away from the surface of the metal ribbon. The punches are guided through a stripper plate which is located just above the metal ribbon which is to be punched, the stripper plate, or a similar element being pressed by spring pressure against the metal ribbon. The stripper plate may have guide openings to guide the punch, and retains the metal ribbon or workpiece blanks in position while permitting movement of the strip tape or ribbon as it is fed between punching strokes.
Machines of this type are well known, and used, primarily, to make various types of punched elements. They are used specifically to make contact plates, contact ribbons, contact elements and the like. With increasing miniaturization of electrical and electronic components, contact terminals which are punched also must be reduced in size. The punch configuration then becomes complex with extremely narrow contact paths remaining between punched openings. Such complex punched shapes frequently cannot be punched in a single punching stroke or step, but a plurality of punching steps are necessary.
To carry out multiple punching steps, sequentially operating punch apparatus are used which have a matrix with punch die openings corresponding to the respective individual punch shapes to be made. The raw or supplied contact ribbons or plates are guided along the die. The punches for the respective punch shapes are located above the contact ribbons, movable towards the contact ribbon. To prevent tipping or distortion of the contact band upon punching, that is, upon cutting thereof, and lifting of the remainder of the ribbon, after punching, as the punch reciprocates outwardly of the ribbon, a stripper plate is held during the entire punching operation against the upper surface of the contact ribbon through which the punches themselves are guided. The stripper plate is placed on the contact ribbon shortly before the punch touches the upper surface of the ribbon. It is removed from the contact surface only after the punch has completely withdrawn from the contact ribbon itself. When the stripper plate lifts, the remainder of the contact ribbon, after the punching operation is indexed by a step for the next punch. The stripper plate is also used to guide the punches which, for miniaturized components, necessarily will also be extremely thin and require guidance during the power stroke to effect accurate punching.
The individual punch shapes, necessary to make contacting elements, for example, are usually prepared in a single matrix die. This matrix die may have length which extend for example to about 80 cm--roughly under about 3 feet--and may even be longer. Sequential punch operations of this length are difficult to control. Varying the punch shape is not possible. Even minor changes in the punched shape require replacement of the entire die, although only a portion of the punched shape may be changed. The stripper plate, likewise, which moved during the punching operation, may require change. In order to provide sufficient stiffness and stability during the punching operation, the stripper plate must be made thicker and heavier as the machine dimension increases, which, in turn, increases the mass to be moved, or lifted during indexing movement of the workpiece ribbon, which, in turn, reduces the operating speed of the machine. Such stripper plates have the additional problem that it is usually necessary that a single highly skilled tool-and-die maker makes the entire plate, which detracts from versatility of scheduling of work in a shop.
It has been proposed to construct apparatus for sequential punching in modular form, see, for example, a report of a conference "Punching Techology - 76", published by the VDI publisher (Publication Office of the Society of German Engineers) entitled "Systematische Sicherung der Werkzeugqualitat" ("Systematic Assurance of Quality of Tools"). The individual work stations, which are necessary to obtain the desired punch configuration are combined in functional groups. For each group, a small and entirely independent tool is made, having its own upper and lower portion, working plate, guide posts and the like. The respective tool units, which form the punches, are then associated. Each such work station has modular plates which are associated with the respective punch shapes. The modular plates are made in the form of inserts which are located in a base structure adjacent each other, to be readily and quickly separable and interchangeable.
The structure has manufacturing advantages, but carries with it the disadvantage that a substantial larger number of the expensive and accurately machined guide posts are required, both base on the subdivision of the working station in functional groups, as well as the necessary increase in numbers due to the individual construction of the work station elements. The association of the respective work stations requires additional attachment connections, so that the coupling of associated modular plates requires additional length of the apparatus. The overall length of machines of this type, constructed in modular technology, is substantially increased with respect to a sequential punch operation having only a single stripper plate. The modular construction has the advantage that the individual modular plates can be changed, and remanufactured if the punch shape changes and, if the punch shape is such that malfunction or disturbances are expected, spare plates can be easily exchanged in connection with maintenance work, or when a malfunction actually occurs, without extensive and expensive down time of the machines. If specific modular are expected to have malfunctions, defects, or require frequent resharpening of punches, spare modules for replacement can be built. In case of malfunction or resharpening of a module in the punch unit, it is then possible to change the respective module quickly.
Additionally, the respective modular inserts of the plates are smaller, lighter in weight, and easier to handle. They can be made independently of each other, independently maintained and repaired. The individual stripper plates likewise are smaller and lighter. The springs necessary to lift and counteract weight of the plates can be made with lesser spring contents and weaker. Since the mass to be moved at each work station also is decreased, the punching frequency can be raised and apparatus of this type can operate with a stroke frequency of up to about 2,000 strokes per minute, corresponding, roughly, to a frequency of 33 Hz.